An investigation into textile applications of thermochromic pigments

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Abstract

Methods were developed for application of thermochromic pigments to textiles, based
on printing and extrusion, for both leuco dye based and cholesteric liquid crystal
thermochromics. The leuco dye based thermochromics were assessed in terms of heat
stability, binder optimization and colour saturation using an instrumental colour
measurement system. Enhancement of lightfastness of leuco dye based thermochromics
was carried out using UV absorbers, HALS and antioxidants as additives. A
comparative study was also carried out between printing and extrusion application
methods. A colour measurement system with the facility for temperature variation was
constructed using two traditional components – a reflectance spectrophotometer and a
controllable hot stage. The dynamic colour change of leuco dye based thermochromics
with temperature was assessed. The liquid crystals were assessed with temperature for
their additive colour mixing properties by layering them over each other. They were
also assessed in terms of aspects of applications, such as differences in the over-layering
sequence and colour hysteresis on heating and cooling. The results were evaluated not
only to provide a scientific understanding of the performance but also to provide useful
information from a creative designer’s point of view.
The research carried out as described in this thesis has established an improved
understanding of the application methods for leuco dye based and liquid crystal
thermochromic pigments for optimum performance. The availability and selection of
colours achievable with liquid crystal thermochromics have been widened significantly
by the improved understanding of the colours derived from over-layered liquid crystals.
It is anticipated that this research will broaden the potential for use of leuco dye based
and liquid crystal thermochromics in textiles, especially in the fields of functional
textiles and creative design.